Direction for traffic remaining behind castle (4,4)

I believe the answer is:

keep left

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'direction for traffic' is the definition.
I don't know anything about this answer so I can't tell whether this works.

'remaining behind castle' is the wordplay.
'remaining' becomes 'left' (synonyms).
'behind' means one lot of letters go next to another.
'castle' becomes 'keep' (I've seen this in other clues).
'left' after 'keep' is 'KEEP LEFT'.

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